Ignition system for internal combustion engines

ABSTRACT

An ignition system of a capacitor discharging type for internal combustion engines having a DC-DC converter, a discharging capacitor, an ignition coil and a silicon-controlled rectifier. In the system, a differentiation circuit, a waveform shaping circuit and a switching element are additionally provided so that the switching element interposed in the base-emitter circuit of an oscillation transistor in the DC-DC converter is actuated by the output pulse from the waveform shaping circuit to cease the operation of the DC-DC converter for a period of time corresponding to the duration of the pulse.

United States Patent Inventors Kazuo Oishi;

Tokuhiro Kurebayashi, both of Kariya-shi, Japan Appl. No. 846,3"

Filed July 31, I96) Patented Aug. 17, I971 Assignec Nippon DensoKabushiki Kaisha I Kariya-shi, Japan Priority Aug. 22, 1968 Japan43/6015 1 IGNITION SYSTEM FOR INTERNAL COMBUSTION ENGINES 6 Claims, 3Drawing Figs.

US. Cl 123/148 E, 3 15/209 56] References Cited UNITED STATES PATENTS3,418,988 12/1968 Lewis eta] 123/148 Primary Examiner-Laurence M.Goodridge Au0rneyCushman, Darby & Cushman PATENTEU AUG I 71971 SHEET 1BF 2 FIG! INVENTORS Kazuo 01 6 31M516 khrabayaslwi BY [u ATTORNEYSIGNITION SYSTEM FOR INTERNAL-COMBUSTION ENGINES BACKGROUND OF THEINVENTION engines.

2. Description of the Prior Art Operation of prior art ignition systemsof the capacitor discharging type has been such that the voltage of astorage battery is st'epped up by means of a DC-DC converter so as tocharge a discharging capacitor by the steppedup voltage, the chargestored in the discharging capacitor is, discharged through'a primarywinding of a ignition coil and a silicon controlled rectifier at theproper ignition time of the engine, and a high voltage thereby inducedin a secondary winding of the ignition coil is applied to a spark plugfor generating a spark across the spark gap of the spark plug.

However, the prior art ignition systems described above .have beendefective in that, as soon as the discharging capacitor completes itsdischarge, the DC-DC converter starts to charge the dischargingcapacitor to prepare for the next ignition and thus thesilicon-controlled rectifier cannot be properly turned off. SUMMARY OFTHE INVENTION In an attempt to overcome the above defect encounteredwith the prior art ignition systems, it is a primary object of thepresent invention to provide an ignition system of the capacitordischarging type for internal combustion engines having a DC-DCconverter, a discharging capacitor charged by the output from said DC-DCconverter, an ignition coil interposed in the discharge circuit of saiddischarging capacitor, and a silicon-controlled rectifier for openingand closing said discharge circuit, said ignition system comprising adifferentiation circuit for detecting a variation in the voltage acrosssaid discharging capacitor during the discharging period of the latter,a waveform shaping circuit for shaping the output from saiddifferentiation circuit into a rectangular waveform, and a switchingelement interposed in said DC-DC converter, said switching element beingactuated by the output pulse delivered from said waveform shapingcircuit so as to cease the operation of said DC-DC converter for aperiod of time which corresponds to the duration of the pulse, wherebysaid silicon-controlled rectifier completes its turned-off state duringthe period of time in which said DC-DC converter is held in itsnonoperative state.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is an electrical connectiondiagram of an embodiment of the ignition system for internal combustionengines according to the present invention;

FIG; 2 is a block diagram showing schematically the structure of thesystem of the present invention,

FIG. 3 is a graphic representation of electrical characteristics forillustrating the operation of the system according to the presentinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1, theignition system according to the present invention comprises a storagebattery 1 which is a power source, a main switch 2, a step-uptransformer 3 having a primary winding 4, a secondary winding 5 and afeedback winding 6, an oscillation transistor 7 for performing ablocking oscillation function, a resistor 8 and a capacitor 9constituting a feedbackcircuit, a biasing resistor 10 for the transistor7, a high-voltage pulse absorbing capacitor 11, a rectifying'diode l2and a discharging capacitor 13. An ignition'coil 14 has a primary'wining15 and a secondary winding 16, and a spark plug 17 is connected to thesecondary winding 16 of the ignition coil 14. A silicon-controlledrectifier 18-interrupts'the primary current in the ignition coil 14. Theprimary winding 15 of the ignition coil 14 has one end thereof connectedto one terminal of the discharging capacitor 13 and the other endthereof is connected to the anode of the silicon-controlled rectifier18, while the cathode of the silicon-controlled rectifier 18 isconnected to the other terminal of the discharging capacitor 13 toconstitute a discharge path for the discharging capacitor 13. A diode 19supplies to the primary winding 15 a current which is in reversedirection to the current passing through the silicon-controlledrectifier l8, and a choke coil 20 which regulates the period of time offlow of the reverse current. A capacitor 21 constitutes together withresistors 22 and 23 a differentiation circuit which detects a variationin the voltage appearing across the discharging capacitor 13. Theignition system further comprises a biasing resistor 24, areverse-voltage preventive diode 25, a differentiated pulseamplifyingtransistor 26, a load resistor 27 for the transistor 26, a capacitor 28for transmitting to the next stage the output pulse appearing at thecollector of the transistor 26, resistors 29 and 30 for dividing thevoltage appearing across the discharging capacitor 13, a Zener diode 31,a biasing resistor 32, an amplifying transistor 33, a load resistor 34for the transistor 33, a coupling resistor 35, a biasing resistor 36, aphase inversion transistor 37, and a switching element 39 in the form ofa transistor which is provided to short circuit the. base and emitter ofthe oscillation transistor 7. The switching element 39 may be asilicon-controlled rectifier in lieu of a transistor.

FIG. 2 is a block diagram of the system according to the presentinvention having a structure as shown in FIG. 1. Operation of the systemaccording to the present invention will be described with reference toFIG. 2. A DC-DC converter 40 constituted by the circuit elements 3 to 12is operative to oscillate, step up, and rectify the voltage of thestorage battery 1 so as to convert such voltage into a high DC voltagewhich is then stored in the discharging capacitor 13. The distributorpoints are opened at the proper time of engine ignition so that thetiming circuit is operated to supply a signal to the silicon-controlledrectifier 18. When the signal is supplied to the gate of thesilicon-controlled rectifier 18 at the proper time of ignition of thefuel-air mixture in the engine and the silicon-controlled rectifier 18is thereby turned on, the charge stored in the discharging capacitor 13is discharged through the primary controlled rectifier 18. At thisinstant, a high voltage is induced in the secondary winding 16 of theignition coil 14 and is applied to the spark plug 17 to make a sparkjump across the gap of the spark plug 17. In the meantime, adifferentiation circuit 41 constituted by the circuit elements 21 and 23detects a variation in the voltage across the discharging capacitor 13during the discharge of the latter. A waveform shaping circuit 42constituted by the circuit elements 24 to 28 delivers a pulse ofrectangular waveform when it receives such a voltage variation. Thepulse is applied to the base of the transistor 39 to urge the transistor39 to its conducting state. As a result, a short circuit is effectedbetween the base and emitter of the oscillation transistor 7 so that theDC-DC converter 40 ceases its operation during the period of timecorresponding to the pulse duration of the pulse.

The above operation will be described in more detail with reference toFIG. 3. In FIG. 3(a), the horizontal axis represents time t and thevertical axis represents voltage Vc across the discharging capacitor 13.In FIG. 3b, the horizontal axis represents time t and the vertical axisrepresents pulse voltage Vp. Up to time t=tp at which the pulse comingfrom the waveform shaping circuit 42 disappears, the DC-DC converter 40is held in its nonoperative state and the voltage Vc across thedischarging capacitor 13 is kept constant. In this connection, it willbe noted that the value of the voltage Vc across the dischargingcapacitor 13 is kept constant from time t, to 2,, of the fact that theDC-DC converter 40 is not in operation. When the silicon-controlledrectifier 18 is turned on, the charge stored in the dischargingcapacitor 13 is completely discharged through the primary winding 15 ofthe ignition coil 14 and through the silicon-controlled rectifier 18.After the charge in the discharging capacitor 13 reaches a maximum valueof polarity opposite to the polarity initially charged therein, thecharge of opposite polarity is discharged by way of the following twodischarge circuits. The first discharge circuit includes the choke coil20, the diode 19 and the primary winding 15 of the ignition coil 14.Since the first discharge circuit has a very low combined impedance, thegreater portion of the chargeof inverted polarity in the dischargingcapacitor 13 is discharged through the first discharge circuit. Thesecond discharge circuit includes the secondary winding 5 of the stepuptransformer 3 and the diode 12. This second discharge circuit serves tocharge the discharging capacitor 13 by the output from the DC-DCconverter '40. If the DC-DC converter is still in operation even afterthe charge in the discharging capacitor has been reversed, the outputfrom the DC-DC converter 40 would positively charge the dischargingcapacitor 13 to cancel out the charge of inverted polarity in thedischarging capacitor 13 with the result that a reverse bias voltagewhich is sufficient to turn off the silicon-controlled rectifier 18would not be obtained. Further, the current output flowing from theDC-DC converter 40 through the diode 12 is a forward current for thesilicon-controlled rectifier l8 and such a current would have asubstantial effect on the failure of the siliconcontrolled rectifier 18to turn off. However, according to the present invention, failure toturn off of the silicon-controlled rectifier 18 by the above phenomenondoes never occur for the following reason. The differentiation circuit41 detects a variation in the voltage across the discharging capacitor13 due to the" initial discharge and a pulse of a rectangular waveformis thereby delivered from the waveform shaping circuit'42 to urge thetransistor 39 to conduct, thereby stopping the operation of the DC-DCconverter 40 is held in its nonoperative state ranges from i=t, at whichtime the charge in the discharging capacitor 13 after polarity inversionhas been turned positive again to i=1 at which time the pulse of therectangular waveform disappears, the voltage Vc across the dischargingcapacitor 13 is held constant between time i=1, and time r=:,,. Thus, upto time r=!, at which the discharging capacitor 13 is dischargedinitially is charged to positive polarity again after taking a maximumvalue of opposite polarity, voltage is applied to the silicon-controlledrectifier 18 in a direction in which a reverse current flows. It willtherefore be understood that the silicon-controlled rectifier 18 can bepositively turned off when the operation of the DC-DC converter 40 iscarried out in the manner described above. Thus, the voltage Vc acrossthe discharging capacitor 13 is kept constant during the time periodrepresented between t, to I In this manner, the DC-DC converter 40 isheld in its nonoperative state for an additional period of time beyondtime t=t, atwhich the current tends to flow in the forward direction ofthe silicon-controlled rectifier 18. However, at time t=t,, thesilicon-controlled rectifier 18 has already been turned off and wouldnot be turned on again until an ignition signal is supplied to the gatethereof. In other words, since the DC-DC converter 40 is held in itsnonoperative state, no current flows from the DC-DC converter 40 throughthe siliconcontrolled rectifier 18 up to time Pt, and thus thesilicon-controlled rectifier 18 is positively turned off.

A constant-voltage control circuit 43 constituted by the circuitelements 29 to 38 operates in such a manner that the resistors 29 and 30and the Zener diode 31 therein detect the voltage across the dischargingcapacitor 13 so that the transistor 39 is urged to conduct to forcedlycease the operation of the DC-DC converter 40 when the voltage acrossthe discharging capacitor 13 exceeds a predetermined setting which isdetermined by the resistors 29 and 30 and the Zener diode 31. Thus, thevoltage across the discharging capacitor 13 can be controlled at aconstant voltage which is sufficient to make a spark jump across thespark gap of the spark plug 17. t

From the foregoing description, it will be understood that the presentinvention provides an ignition system of the capacitor discharging typefor internal combustion engines having a DC-DC converter, a dischargingcapacitor charged by the output from said DC-DC converter, an ignitioncoil interposed in the discharge circuit of said discharging capacitor,and a silicon-controlled rectifier for opening and closing saiddischarge circuit, said ignition system comprising a differentiationcircuit for detecting a variation in the voltage across said dischargingcapacitor during the discharging period of the latter, a waveformshaping circuit for shaping the output from said differentiation circuitinto rectangular waveform, and a switching element interposed in thebaseemitter circuit of an oscillation transistor in said DC-DCconverter, said switch element being actuated by the output pulsedelivered from said waveform shaping circuit so as to cease theoperation of said DC-DC converter for a period of time which correspondsto the duration of the pulse, whereby said silicon-controlled rectifiercompletes its turned-off state during the period of time in which saidDC-DC converter is held in its nonoperative state.

What is claimed is:

1. An improved ignition system of the capacitor discharging type forinternal combustion engines including a DC-DC converter having anoscillator therein, a discharging capacitor which is charged by anoutput of said DC-DC converter, an ignition coil disposed in adischarging circuit of said discharging capacitor and asilicon-controlled rectifier connected in series with said dischargingcapacitor and a primary winding of said ignition coil, wherein saidrectifier is more effectively switched off at the completion of adischarge cycle, said improved system comprising:

a differentiation circuit for detecting a variation in a voltage acrosssaid discharging capacitor during a discharging period of saiddischarging capacitor,

a waveform shaping circuit for shaping an output of said differentiationcircuit into a rectangular waveform, and

a switching element disposed in a circuit of said oscillator in saidDC-DC converter, said switching element being actuatable by saidrectangular waveform for stopping the operation of said oscillatorthereby substantially eliminating said output of said'DC-DC converterfor a period of time corresponding to the duration of said rectangularwaveform thus insuring that said rectifier may be positively turned offafter said discharging period.

2. An ignition system as in claim 1 wherein said DC-DC convertercomprises:

a transformer having a primary winding, a secondary winding and afeedback winding, and

a blocking oscillator circuit including a transistor and a parallelconnection of a resistor and a capacitor.

3. An ignition system as in claim 1 wherein a series connection of aninductance for contributing to the extinguishment of saidsilicon-controlled rectifier and a reversed current preventative diodeis connected in parallel with said silicon-controlled rectifier.

4. An ignition system as in claim 1 wherein said waveform shapingcircuit and said switching element are connected with each other viacapacitor and said ignition system further comprises a constant-voltagecontrol circuit which is operated by a voltage across terminals of saiddischarging circuit for generating a signal voltage and for energizingsaid switching element when said voltage exceeds a predetermined value.

5. An ignition system as in claim 2 wherein said switching elementcomprises a transistor for establishing an effective short circuitbetween base and emitter electrodes of transistor in said oscillator.

6. An improvement for use in a capacitor dischargeignition systemcomprising a controlled rectifier in capacitor discharge circuit and aDC-DC converter which includes an oscillator means, said improvementcomprising:

differentiation means connected to said discharge circuit for detectinga discharge period signified by a rapid voltage variation therein,

waveform shaping means connected to said differentiation means forproducing an output signal in response to the detectionof said dischargeperiod, and

and for thereby substantially eliminating a DC output of said DC-DCconverter and causing substantial cessation of current flow through saidcontrolled rectifier.

1. An improved ignition system of the capacitor discharging type forinternal combustion engines including a DC-DC converter having anoscillator therein, a discharging capacitor which is charged by anoutput of said DC-DC converter, an ignition coil disposed in adischarging circuit of said discharging capacitor and asilicon-controlled rectifier connected in series with said dischargingcapacitor and a primary winding of said ignition coil, wherein saidrectifier is more effectively switched ''''off'''' at the completion ofa discharge cycle, said improved system comprising: a differentiationcircuit for detecting a variation in a voltage across said dischargingcapacitor during a discharging period of said discharging capacitor, awaveform shaping circuit for shaping an output of said differentiationcircuit into a rectangular waveform, and a switching element disposed ina circuit of said oscillator in said DC-DC converter, said switchingelement being actuatable by said rectangular waveform for stopping theoperation of said oscillator thereBy substantially eliminating saidoutput of said DC-DC converter for a period of time corresponding to theduration of said rectangular waveform thus insuring that said rectifiermay be positively turned off after said discharging period.
 2. Anignition system as in claim 1 wherein said DC-DC converter comprises: atransformer having a primary winding, a secondary winding and a feedbackwinding, and a blocking oscillator circuit including a transistor and aparallel connection of a resistor and a capacitor.
 3. An ignition systemas in claim 1 wherein a series connection of an inductance forcontributing to the extinguishment of said silicon-controlled rectifierand a reversed current preventative diode is connected in parallel withsaid silicon-controlled rectifier.
 4. An ignition system as in claim 1wherein said waveform shaping circuit and said switching element areconnected with each other via capacitor and said ignition system furthercomprises a constant-voltage control circuit which is operated by avoltage across terminals of said discharging circuit for generating asignal voltage and for energizing said switching element when saidvoltage exceeds a predetermined value.
 5. An ignition system as in claim2 wherein said switching element comprises a transistor for establishingan effective short circuit between base and emitter electrodes oftransistor in said oscillator.
 6. An improvement for use in a capacitordischarge ignition system comprising a controlled rectifier in capacitordischarge circuit and a DC-DC converter which includes an oscillatormeans, said improvement comprising: differentiation means connected tosaid discharge circuit for detecting a discharge period signified by arapid voltage variation therein, waveform shaping means connected tosaid differentiation means for producing an output signal in response tothe detection of said discharge period, and switch means connected fromsaid waveform shaping means to said DC-DC converter for causing saidoscillator means to be inoperative in response to said output signal andfor thereby substantially eliminating a DC output of said DC-DCconverter and causing substantial cessation of current flow through saidcontrolled rectifier.